An image sensor can be used to capture digital image data. The image sensor is formed by arrays of photo sensors, for example, charge coupled device (CCD) sensors or CMOS sensors. One photo sensor captures data associated with one pixel of image data. Increasing the number of photo sensors used to capture a digital image increases the quality of the digital image.
Image sensors are manufactured in silicon chips and include millions of individual photo sensors arranged in arrays. Individual photo sensors are small and have submicron features. These submicron features can make producing a defect free array of photo sensors on a silicon chip difficult. Defective sensors include regions that display either increased dark current, electrical faults or variations in sensitivity. The type and number of defective photo sensors is often used as a screening mechanism in the manufacturing process of chips with image sensors. Silicon chips with too many defective photo sensors are not usable and are not marketable. The type and number of defective photo sensors may influence both chip yield and the price of a silicon chip.
There are different kinds of defects that can occur on an image sensor. Defects include isolated point defects, cluster defects, and row/column defects. In addition to these defects, a defective photo sensor can generate defective pixels that have a non-uniform response with respect to neighboring pixels.